1. Field of the Invention
The present invention relates to a printer assembly and a printer for printing on a thermal paper of sheet.
2. Description of the Related Art
Computers are used for many applications, and along with the development of them, various types of printer are required as a peripheral device for output. Conventionally, when the computer was large and could not be moved, printers were large for having a fast processing speed. On the contrary, as personal computers such as a desktop type or the like become popular, printers become small, and desktop size printers have become popular.
Recently, various types of computers have been developed and used. Portable type computers are also developed such as a notebook type to a portable or mobile type such as PDA, that has a size easily put in a pocket. Moreover, as the Internet becomes popular, applications of the computer are widespread in various fields such as information service and communication, and the variation of users are so wide from a specialist to a general user. It is considered that as the population of users increases in the future, computers will be used in daily life in ordinary homes. In addition, the applications of computers are advancing in the direction of handling daily works with a computer at home, such as computerized account settlement, electronic commerce.
As the applications of the computer and the population of users expand, development of a printer for the various users is desired. There is an opinion that the usefulness of prints has decreased as the information and communication are computerized, however, there is a demand at all times for outputting the information obtained by a computer, history of communication and reports of account settlement in the form of printout for confirmation and for storing it temporarily. Moreover, printers being able to connect to portable phones will be required.
As the computer or other mobile equipments increase, it is desired that a printout can be available at any time when desired. Moreover, in a case where a computer is used for daily work such as electronic commerce/transactions or the like, the quantity of information to be printed out is small, and the frequency of using a printer may be low. For such a user, it will be important that the expense for buying a printer is small, and it will be an important factor that a space for installing a printer is not necessary or very small. Demand for a small and lightweight printer is so large among the users of a portable-type computer such as PDA or the portable phone.
Therefore, it is certain that one style desired as a future printer will be thin, compact, lightweight and low-cost. A printer for printing on a thermal (thermosensitive) paper using a thermal head does not require an ink nor ribbon, hence the printing mechanism can be made compact. In particular, a line thermal printer having line thermal head that is a thermal head extending in the paper width direction (in the scanning direction or the line direction), can be made very compact, since a mechanism for moving the thermal head in the scanning direction is not necessary. Hence it is suitable for the above-described demand.
However, in order to realize a printer having a thickness of about 10 mm or less, a mechanism for pushing a printing paper against the thermal head becomes a big problem. Conventionally, a thermal paper is pressed between the thermal head and a platen roller, and the platen roller is rotated. Therefore, the thermal paper is fed while being pressed against the thermal head. To realize a thin printer, it is necessary to reduce the diameter of the platen roller, but if the diameter of the platen roller is made small, the contact area becomes insufficient. Therefore, in order to push or press the printing paper against the thermal head with a predetermined force, it is necessary to press the platen roller with a stronger force. However, if the diameter of the platen roller is made 10 mm or less, the strength of the platen roller becomes insufficient, hence if a pushing force or pressure is increased, distortion or bend is likely to occur.
Moreover, if the diameter of the platen roller becomes 5 mm or less, distortion occurs, hence the platen roller cannot push the printing paper against the thermal head with a uniform force. In particular, when the printer is a line thermal printer, if a force for pressing the thermal paper against the line thermal head differs in the paper width direction, or if a pressure is partly insufficient, the printing quality is deteriorated, and printing becomes impossible.
Such distortion or bend of the roller may be prevented if the roller is divided in the longitudinal direction to expose a shaft of roller and the exposed parts of the shaft are supported by a plurality of bearings. In the case of a platen roller, however, since it is necessary to apply a uniform pressure in the scanning direction, that is longitudinal direction of the roller, the roller cannot be divided in the longitudinal direction. Hence, the above solution cannot be adapted to the platen roller. It is also possible to support a platen roller (rotating body) by several sub rollers disposed in the longitudinal direction to prevent bending or distortion of the platen roller. However, additional thickness is required for installing the sub rollers, hence the second solution is not adaptable to a thin printer.
Under such circumstances, the present inventor has developed a technology for realizing a card-type thermal printer having a thickness of 5 mm or less. As a result, a technology that can clear the above-described problems relating to the platen roller has been developed and a very thin printer having a high printing quality becomes possible.
That is to say, it is an object of the present invention to provide a printing mechanism, that is, a printer assembly, that can reduce the thickness of a line thermal type printer about 10 mm or less, preferably, about 5 mm or less. A further object is to provide a printer having a thickness of 10 mm or less, preferably about 5 mm or less.
A printer assembly of the present invention, a stationary type platen, that is, a platen or a pressure plate-type platen that does not rotate like a roller is used for pressing a printing paper against a thermal head. In addition, a paper feed or extracting device is provided on the paper ejection side of the non-roller type platen for extracting or pulling the printing paper. The printer assembly of the present invention has a line thermal head extending in the paper width direction, a non-roller type platen disposed so as to face the line thermal head for pressing a thermal paper between the line thermal head and the platen, and a paper extracting device disposed on a paper ejection side of the line thermal head (hereinafter sometimes referred to as xe2x80x9cthermal headxe2x80x9d) and the platen, the paper extracting device having first and second rollers for extracting the thermal paper between the first and second rollers.
As the non-roller type, it is desired to have a section of a shape tapered toward the thermal head, not a circular shape, such as a semi-circular shape or a trapezoidal shape with the thermal head side becoming narrow. The one side of such shape of platen can be supported easily by a housing or the like, and the other side is pushed against the thermal head. Therefore, adopting an elastic body having the section of above as the platen, reliably apply a predetermined force for pressure to the printing paper. In addition, it is preferable that at least a portion facing the line thermal head is covered with a covering material having a low coefficient of friction, for example, a fluoro resin type material such as Teflon (trademark). By the platen of this invention, a force for pressing the thermal paper against the thermal head can be obtained and the frictional resistance at the time of paper feed can be made small even with the non-roller type platen.
The platen having a plate or a keep plate with a surface having a small coefficient of friction and facing the line thermal head, and an elastic member for pressing the plate in the direction of the line thermal head can press the thermal paper against the thermal head as described above while reducing a frictional force at the time of paper feed.
With such a kind of non-roller type platen, some supporting frame, member or the housing can support the entire platen extending in the paper width direction. Therefore, even if the sectional area of the platen itself is not so large, and the platen itself does not have a high strength, distortion or bend does not occur by a strong force (pressure), or distortion becomes minimum. Hence, if there is a thin space of several millimeters or less facing the thermal head, a printing paper can be pressed with a sufficient force uniformly in the paper width direction against the thermal head by the non-roller type platen. Therefore, a printer assembly having a high printing quality can be realized, even if it is thin.
Contrary, in the paper extracting device provided on the paper ejection side of the thermal head, if a sufficient force for pulling or extracting the printing paper inserted between the thermal head and the platen can be obtained, it is not necessary to apply a uniform pressure continuously to the paper in the paper width direction. Therefore, according to the requirement to make the roller diameter 10 mm or less, particularly, 5 mm or less, a construction is adopted that the rotating body (roller) is divided into a plurality of rollers to expose the shaft, and the exposed parts of shaft located middle of the width direction are supported by a plurality of bearings between the rotating bodies. Hence, if the strength is insufficient due to the small roller diameter, the distortion of rollers in the extraction device will be prevented easily. By adopting such construction for at least one of the first and second rollers or for both rollers of the extracting device, a force for reliably feeding or extracting the paper without distortion can be obtained and the rollers can be installed in a thin space.
Therefore, according to the present invention, a printer assembly capable of pressing a printing paper against the thermal head with a sufficiently, and capable of obtaining a predetermined paper feeding force stably can be made very thin. The entire thickness of the printer assembly of this invention can be reduced to less than about 10 mm, preferably, to less than about 5 mm.
Accordingly, by combining the printer assembly of the present invention and a paper feed mechanism for feeding a thermal paper to the printer assembly, a very thin and compact printer having a thickness of less than about 10 mm, preferably, less than about 5 mm can be provided.
In addition, in the thermal type printer, since consumables such as an ink or the like is not required and the space is not necessary, it is possible to make the entire printer so thin by adopting the stationary type platen. Hence, printer having an overall thickness as thin as a card is realized.
In order to print by the printer assembly of the invention, first it is necessary to pass the tip of a printing paper between the thermal head and the platen and insert the tip of the paper between the rollers of the extracting device. It is desired to provide a first frame for supporting the thermal head, a second frame for supporting directly of indirectly the platen, and a gap forming mechanism for opening the space between the first frame and the second frame. It is possible to open (give a gap) between the thermal head and the platen by the gap forming mechanism to feed a printing paper to the extracting rollers, then to close the gap between the thermal head and the platen to press the printing paper between the thermal head and the platen to getting the high quality printout.
It is preferable that the first frame supports the first roller and the second frame supports the second roller. A gap control between the first and second rollers can be performed simultaneously by the gap forming mechanism. As the gap forming mechanism, a cam member that moves between the first frame and the second frame can be used.
In the platen having the plate pressing against the line thermal head with an elastic member, by depressing the plate or the elastic member, it is possible to make the gap between the platen and the thermal head.
When a gap is not formed by the gap forming mechanism, the force to press the thermal paper against the thermal head can be obtained by the elastic body of the platen itself or the elasticity of the elastic member. It is also possible to provide a pressing mechanism for ensuring the pressure between the thermal head and the plate also between the first and second roller of the extracting device. One of the pressing mechanisms is a spring member elastically connecting the first and second frames.
In the printer for the sheet or cut sheet type thermal paper not for the roller type thermal paper, the paper feeding mechanism comprises a pickup roller for pick up the thermal paper and a bottom plate for pressurizing the thermal paper to the pickup roller. The friction or pressing force between the pickup roller and the bottom plate may become a resistance force during the printing or feeding the paper by the extracting device. Therefore, it is preferable to apply a depressing mechanism for depressing the bottom plate when the thermal paper feeding by the extracting device. By the depressing mechanism, a phenomenon that the surface of the thermal sheet shines by the friction is prevented. If the printer assembly has the gap forming mechanism, the depressing mechanism for depressing the bottom plate linked with the gap forming mechanism is useful. The gap forming mechanism comprises a cam member for forming the gap between the platen and the line thermal head at one position and forming a gap between the pickup roller and the bottom plate at another position.
Furthermore, to prevent respective distortion of the first and second rollers by means of the first and second frames, it is desirable that the first and second rollers comprise a plurality of rotating bodies divided in the paper width direction and a shaft for connecting these rotating bodies, respectively, and the first and second frames be respectively provided with a plurality of bearings for respectively supporting the shaft of the first roller and the shaft of the second roller between the rotating bodies.